During semiconductor fabrication (i.e., the process of creating integrated circuits on a silicon wafer for use in electronic devices), or more generally workpiece processing (e.g., flat panel display processing, lithography mask processing, etc.) a given substrate (e.g., silicon) may be exposed to a multitude of different sub-processes before the final product is completed. By way of example, and not by way of limitation, in the context of semiconductor fabrication, these sub-processes may include deposition, removal, patterning, and modification of electrical properties.
Deposition involves any process that grows, coats, or otherwise transfers a material onto the substrate. Several technologies exist for deposition depending on the nature of deposition desired. These technologies include physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE), and atomic layer deposition (ALD). Removal involves any process that removes material from the wafer. Again, several technologies exist for removal depending on the type of removal desired (e.g., bulk, selective, etc.). These technologies include wet etching, dry etching, chemical-mechanical planarization (CMP) and plasma ashing. Finally, several different techniques exist for patterning (i.e., modifying the existing shape of deposited material) and modification of electrical properties and thermal properties (e.g., doping, annealing). Many of these sub-processes require the use of certain workpiece processing tools to facilitate performance.
To ensure effective design, process optimization, and fault detection of these workpiece processing tools, it is important to track certain characteristics and processing conditions associated with those tools. In particular, the heat flux developed through a substrate by a workpiece processing tool during operation may provide crucial information that aids in maintaining quality assurance and consistent controlled performance of the workpiece processing tool and very sub-process it is designed to serve. Moreover, measurement of localized spatial differences in heat flux as a function of time can provide means by which these workpiece processing tools and processes may be characterized independent of workpiece variability.
Currently, very few techniques exist for determining heat flux through a substrate. Those techniques that do exist possess limitations that make them impractical for use in particular workpiece processing tools. One technique uses the thermal decay rate of a temperature sensor to calculate heat flux. This technique is described, e.g., in commonly-assigned U.S. Pat. No. 6,907,364, which is incorporated herein by references. To employ this technique, a thermal stimulant is initially applied to a temperature sensor located on a substrate. The thermal stimulant is then turned off, and the temperature decay of the temperature sensor is measured, ultimately resulting in the determination of heat flux. This technique, however, is impractical for implementation with certain workpiece processes (e.g., standard wafer production processes). This is because continuous monitoring of the rate of change of heat flux cannot be realized using this technique and sporadic, transient monitoring may not supply the intended benefit.
A second technique involves embedding commercially available heat flux sensors in device substrates. However, these sensors are typically available only in large sizes (centimeters in length), and may not meet the dynamic range required for certain applications. The introduction of additional structures to the surface of a substrate during processing has the potential to cause severe disturbances in process conditions in a workpiece processing tool. Additionally, many of the materials used to construct these heat flux sensors may be incompatible with particular processing tools or processes. Thus, integrating these heat flux sensors into wafer like substrates for determining process conditions in a workpiece processing tool may be extremely challenging.
There is a need in the art for a technique capable of measuring heat flux through one or more locations of a substrate being processed by a workpiece processing tool configured to process production workpieces. It is within this context that embodiments of the present invention arise.